The present invention relates to polymerizable compositions, a process for the preparation thereof, and the use of said compositions as dental compositions.
It has been known for a long time to make up dental compositions, such as, for example, tooth filling materials, veneer and crown materials, orthodontic base materials, etc., from polymerizable ethylenically unsaturated monomers (usually mono or polyfunctional methacrylic esters), and to mix the latter with fillers to give them essential desired properties. These include obtaining a pasty consistency, adjustment of optical and cosmetic effects, reduction of the polymerization shrinkage, and, if reinforcing fillers are used, improving the mechanical properties such as compressive and flexural strength, and surface hardness, etc.
Apart from inorganic fillers, such as quartz or glasses in finely ground form or dispersive silicic acids, organic fillers are also used. Organic fillers are particularly appropriate when specific processing properties or specific optical effects (e.g. high transparency) or complete combustibility of the material are of significance. As apparent for example from "Skinner's Science of Dental Materials", W. B. Saunders Company 1982, p. 177 et seq., p. 245, bead-like polymers of methylmethacrylate (possibly with slight additions of bifunctional crosslinking monomers) having an average grain size of 20-30 .mu.m are a widely used organic filler. These beads are mixed, for example, with methylmethacrylate and within a few minutes the mixture swells to give a doughy mass which mixed with the usual polymerization initiators, can be formed in suitable hollow molds and subsequently polymerized. However, because of the swelling behavior it is not possible to make monocomponent materials on this basis. Said systems are used inter alia for denture plastics, veneer and crown materials, modelling plastics, and tooth filling materials.
German reference No. 2,850,916 Walkowiak et al. dated June. 12, 1980 corresponding to U.S. Pat. No. 4,369,262-Walkowiak et al. dated Jan. 18, 1983, discloses highly crosslinked bead polymers which hardly swell after mixing with the monomers. However, due to the higher density compared with the monomer component, they have the tendency to sediment in the mixtures so that as a rule inorganic antisedimentation agents must be used to suppress this tendency. This has, however, decisive influence on the optical properties and the complete combustibility of these materials. Moreover, as a rule these polymers do not have a strengthening effect.
In Houben-Weyl, Volume XIV/1, p. 133 et seq., the preparation of voluminous powders by precipitation polymerization from acrylic acid esters is described. A. B. Wojcik specifically described such polymers in Angew, Makromol. Chem. 119, 193 (1983) and 121, 89 (1984). However, not even a hint is given anywhere as to the use of such polymers as fillers in dental materials. The fact that the use of such polymers as fillers in dental materials is not considered in this publication is apparent not least from Houben-Weyl, loc. cit., p. 146 where the following is stated: "Lumpy precipitation or coagulation is a frequently encountered unfortunate secondary effect which must be overcome by variation of the solubility conditions."
One object of the present invention is to provide an organic filler for compositions, in particular dental materials, containing (meth)acrylic esters which exhibits practically no swelling behavior, has a strengthening effect, and permits the preparation of stable non-sedimenting monocomponent preparations. Another object is to retain the optical, mechanical, and toxicological properties essential to dental materials.
These and other objects and advantages of the present invention will appear more clearly from the following specification in conjunction with the accompanying Examples.